Failure determination system, failure determination method and engine control unit for variable-cylinder internal combustion engine

Abstract

There is provided a failure determination system for a variable-cylinder internal combustion engine which is capable of promptly and accurately carrying out failure determination of the valve-actuating system for cylinders for being made idle during a partial-cylinder operation mode. The failure determination system is capable of switching a cylinder operation mode between an all-cylinder operation mode in which all the cylinders are operated, and a partial-cylinder operation mode in which part of the cylinders are made idle. The failure determination system includes an ECU which executes a failure-determining operation mode for causing a valve-actuating mechanism to resume actuation of intake valves and exhaust valves of the part of the cylinders in a state in which fuel supply to the part of the cylinders is stopped, when the cylinder operation mode is shifted from the partial-cylinder operation mode to the all-cylinder operation mode. The ECU determines whether or not the valve-actuating system including the valve-actuating mechanism has failed, based on an oxygen concentration detected when the failure-determining operation mode is executed.

What is claimed is:  
     
       1. A failure determination system for a variable-cylinder internal combustion engine including a plurality of cylinders each having at least one intake valve and at least one exhaust valve, and a valve-actuating system including a valve-actuating mechanism for actuating said at least one intake valve and said at least one exhaust valve of each of said cylinders, said engine being capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of said plurality of cylinders are operated, and a partial-cylinder operation mode in which fuel supply to part of said plurality of cylinders is stopped and at the same time said part of said plurality of cylinders are made idle by stopping said valve-actuating mechanism from actuating said at least one intake valve and said at least one exhaust valve of each of said part of said cylinders, 
       the failure determination system comprising:  
       oxygen concentration-detecting means for detecting a concentration of oxygen in exhaust gases exhausted from said plurality of cylinders;  
       failure-determining operation mode-executing means for executing a failure-determining operation mode for causing said valve-actuating mechanism to resume actuation of said at least one intake valve and said at least one exhaust valve of at least one of said part of said cylinders in a state in which said fuel supply to said part of said cylinders is stopped, when said cylinder operation mode is switched from said partial-cylinder operation mode to said all-cylinder operation mode; and  
       failure determination means for determining whether or not said valve-actuating system including said valve-actuating mechanism has failed, based on an oxygen concentration detected by said oxygen concentration-detecting means when said failure-determining operation mode is executed.  
     
     
       2. A failure determination system according to  claim 1 , wherein said failure determination means determines that said valve-actuating system has failed, when said oxygen concentration is equal to or lower than a predetermined value. 
     
     
       3. A failure determination system according to  claim 1 , wherein said failure determination means determines that said valve-actuating system has failed, when an amount of change in said oxygen concentration in an increasing direction is smaller than a predetermined amount of change. 
     
     
       4. A failure determination system for a variable-cylinder internal combustion engine including a plurality of cylinders each having at least one intake valve and at least one exhaust valve, and a valve-actuating system including a valve-actuating mechanism for actuating said at least one intake valve and said at least one exhaust valve of each of said cylinders, said engine being capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of said plurality of cylinders are operated, and a partial-cylinder operation mode in which fuel supply to part of said plurality of cylinders is stopped and at the same time said part of said plurality of cylinders are made idle by stopping said valve-actuating mechanism from actuating said at least one intake valve and said at least one exhaust valve of each of said part of said cylinders, 
       the failure determination system comprising:  
       an oxygen concentration-detecting module for detecting a concentration of oxygen in exhaust gases exhausted from said plurality of cylinders;  
       a failure-determining operation mode-executing module for executing a failure-determining operation mode for causing said valve-actuating mechanism to resume actuation of said at least one intake valve and said at least one exhaust valve of at least one of said part of said cylinders in a state in which said fuel supply to said part of said cylinders is stopped, when said cylinder operation mode is switched from said partial-cylinder operation mode to said all-cylinder operation mode; and  
       a failure determination module for determining whether or not said valve-actuating system including said valve-actuating mechanism has failed, based on an oxygen concentration detected by said oxygen concentration-detecting module when said failure-determining operation mode is executed.  
     
     
       5. A failure determination system according to  claim 4 , wherein said failure determination module determines that said valve-actuating system has failed, when said oxygen concentration is equal to or lower than a predetermined value. 
     
     
       6. A failure determination system according to  claim 4 , wherein said failure determination module determines that said valve-actuating system has failed, when an amount of change in said oxygen concentration in an increasing direction is smaller than a predetermined amount of change. 
     
     
       7. A method of determining failure of a valve-actuating system of a variable-cylinder internal combustion engine including a plurality of cylinders each having at least one intake valve and at least one exhaust valve, and said valve-actuating system including a valve-actuating mechanism for actuating said at least one intake valve and said at least one exhaust valve of each of said cylinders, said engine being capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of said plurality of cylinders are operated, and a partial-cylinder operation mode in which fuel supply to part of said plurality of cylinders is stopped and at the same time said part of said plurality of cylinders are made idle by stopping said valve-actuating mechanism from actuating said at least one intake valve and said at least one exhaust valve of each of said part of said cylinders, 
       the failure determination method comprising the steps of:  
       detecting a concentration of oxygen in exhaust gases exhausted from said plurality of cylinders;  
       executing a failure-determining operation mode for causing said valve-actuating mechanism to resume actuation of said at least one intake valve and said at least one exhaust valve of at least one of said part of said cylinders in a state in which said fuel supply to said part of said cylinders is stopped, when said cylinder operation mode is switched from said partial-cylinder operation mode to said all-cylinder operation mode; and  
       determining whether or not said valve-actuating system including said valve-actuating mechanism has failed, based on an oxygen concentration detected when said failure-determining operation mode is executed.  
     
     
       8. A method according to  claim 7 , wherein the determining step includes determining that said valve-actuating system has failed, when said oxygen concentration is equal to or lower than a predetermined value. 
     
     
       9. A method according to  claim 7 , wherein the determining step includes determining that said valve-actuating system has failed, when an amount of change in said oxygen concentration in an increasing direction is smaller than a predetermined amount of change. 
     
     
       10. An engine control unit including a control program for causing a computer to carry out determination of failure of a valve-actuating system of a variable-cylinder internal combustion engine including a plurality of cylinders each having at least one intake valve and at least one exhaust valve, and said valve-actuating system including a valve-actuating mechanism for actuating said at least one intake valve and said at least one exhaust valve of each of said cylinders, said engine being capable of switching a cylinder operation mode between an all-cylinder operation mode in which all of said plurality of cylinders are operated, and a partial-cylinder operation mode in which fuel supply to part of said plurality of cylinders is stopped and at the same time said part of said plurality of cylinders are made idle by stopping said valve-actuating mechanism from actuating said at least one intake valve and said at least one exhaust valve of each of said part of said cylinders, 
       wherein the control program causes the computer to detect a concentration of oxygen in exhaust gases exhausted from said plurality of cylinders, execute a failure-determining operation mode for causing said valve-actuating mechanism to resume actuation of said at least one intake valve and said at least one exhaust valve of at least one of said part of said cylinders in a state in which said fuel supply to said part of said cylinders is stopped, when said cylinder operation mode is switched from said partial-cylinder operation mode to said all-cylinder operation mode, and determine whether or not said valve-actuating system including said valve-actuating mechanism has failed, based on an oxygen concentration detected when said failure-determining operation mode is executed.  
     
     
       11. An engine control unit according to  claim 10 , wherein said control program causes said computer to determine that said valve-actuating system has failed, when said oxygen concentration is equal to or lower than a predetermined value. 
     
     
       12. An engine control unit according to  claim 10 , wherein said control program causes said computer to determine that said valve-actuating system has failed, when an amount of change in said oxygen concentration in an increasing direction is smaller than a predetermined amount of change.